Turbulent transition by photon-correlation spectroscopy

The technique of photon-correlation spectroscopy was exploited to study turbulent pipe flow behind a grid. We measure the correlation function g(t) of the light intensity scattered by small particles suspended in the turbulent fluid. The results imply that the probability distribution function for the small relative velocity fluctuations in the turbulent grid flow is Lorentzian-like. The statistical properties of the small velocity fluctuations over varying length scales possess a self-similar feature. This self-similarity was seen only when the Reynolds number becomes larger than a specific value scrRc. All the measurements suggest that the flow changes its character at this point.